JPH03258186A - Recording and reproducing device for video signal - Google Patents

Abstract

PURPOSE:To improve the accuracy of recovered clock and to prevent deterioration in picture quality by increasing a level of a burst signal more than a level of a video signal in a video tape recorder in which a High Vision signal is FM-modulated and recorded and reproduced. CONSTITUTION:A signal level of a burst signal 6 is set larger than a level of a luminance signal 3 by nearly 18dB and set larger than that of a color difference signal 2 by nearly 12dB. Moreover, a peak level of a horizontal synchronizing pulse 5 is set nearly equal to a negative peak level of the signal 6 or set smaller than that. Thus, when the signal level of the signal 6 is set larger in this way, the S/N at the reproduction of the signal 6 is excellent, the accuracy of the recovered clock is improved and no deterioration in the picture quality of the reproduced picture is caused. That is, a write clock WCK with excellent tracking with respect to jitter of the reproduction signal is produced from a write clock generating circuit 37 of the reproduction section 8 and a same output data as an input data to a D/A converter section 17 of a recording section 7 is obtained from an A/D converter 30.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a video signal recording and reproducing apparatus suitable for use in, for example, a video tape recorder that records and reproduces FM-modulated high-definition signals.

[Summary of the invention]

The present invention relates to a video signal recording and reproducing device suitable for use in a video tape recorder that records and reproduces a high-definition signal by FM modulation, for example. In a recording/reproducing device that adds a burst signal within each cycle to generate a reproduction clock when a signal is reproduced by digital signal processing, the level of the burst signal is made higher than the level of the video signal. By improving the accuracy of the reproduced clock, it is possible to prevent deterioration of image quality.

[Conventional technology]

When recording analog video signals with a video tape recorder (VTR), the problem is how to prevent interference between luminance signals and color signals. In conventional video signals with 525 or 625 horizontal scanning lines per frame,
These luminance signals and chrominance signals have been recorded in the form of frequency multiplexing, but in frequency multiplexing, the separation of the luminance signals and chrominance signals during reproduction is not complete, and cross-color interference may occur. Therefore, the number of horizontal scanning lines per frame is 1.
In the case of a high-definition signal that requires high image quality with about 125 lines, for example, the analog three primary color signals R1G and B are each subjected to FM modulation and recorded using different heads. In this case, in a studio VTR, the signal obtained by adding the high frequency part yh of the luminance signal to the G signal is time-expanded twice and recorded using a two-channel head.

On the other hand, in high-definition VTRs for general business or consumer use, the number of channels is reduced and the mechanism is simplified, so the luminance signal Y and color difference signal C (
Pg and P,) are time-division multiplexed and then subjected to FM modulation and recorded using, for example, a two-channel head. The content of the time division multiplexing is that the luminance signal (bandwidth 20MHz) is divided into the color difference signal (bandwidth 7MHz>
By taking advantage of the narrow band of the luminance signal, approximately 2
In this method, a two-channel signal is generated by time-expanding the signal, and at the same time, the color difference signal is time-compressed to approximately 1/4 and multiplexed line-sequentially in the empty portion of each channel. Therefore,
This time-division multiplexed signal is a multiplexed signal that includes time axis compression.
gration) signal.

Such a TCI signal is generally generated by converting an analog input signal into a digital signal, compressing or expanding the signal by digital processing, and then converting the digital signal into an analog signal. In order to reproduce the original luminance signal and color difference signal from the analog TCI signal obtained from the reproduction head and the FM demodulation circuit, the TCI
After converting a signal into a digital signal and performing digital expansion or compression, it is necessary to convert the digital signal back into an analog signal. Therefore, in order to generate a reproduction clock for accurate analog/digital conversion during reproduction, a synchronization pulse and a burst signal are added to the recording signal. Furthermore, generally high-definition VT
In R, TB corrects time axis fluctuations such as jitter and skew.
C (time base collector) is required, and this TB
A synchronization pulse and a burst signal are also added to generate an accurate write clock to C.

Figure 3 shows the FM of a conventional general business or consumer VTR.
This shows the TCI signal for one channel before modulation, and this third
In the figure, (1) is a horizontal synchronizing pulse with a negative polarity and a binary opening period of IH, and this 1H is equal to the horizontal period of the high-definition signal. In addition, (2) is a color difference signal (P, or Pi
), (3) has a width of 0.75, which is approximately doubled in time.
The H luminance signal Y (4) shows a burst signal of about 5 waves with a frequency of approximately 5 MHz, and during the horizontal synchronization pulse (1), these burst signals (4), color difference signal (2), and luminance signal (3) are time-division multiplexed. This burst signal (4
) is approximately an intermediate frequency within the signal band, and is set to m/n times the frequency of the reproduced clock (m and n are integers).

In the example in Figure 3, the S/N ratio of the luminance signal (3) is 41d.
The S/N ratio of the color difference signal (2) is 45 dB or more, and the S/N ratio of the burst signal (4) is about the same as that of the luminance signal (3). Specifically, at the digital signal stage, the difference (signal level) between the black level and white level of the luminance signal (3) and the amplitude (signal level) of the burst signal (4) are both about 6 bits (26), and the difference (signal level) between the black level and white level of the luminance signal (3) is about 6 bits (26), The maximum amplitude (signal level) of 2) is set to about 6 to 7 bits (26 to 27). Furthermore, the average level of the color difference signal (2) and the DC level of the burst signal (4) are both set higher than the average level of the luminance signal (3). The TCI signal in the example shown in FIG. 3 is emphasized, then FM modulated and recorded on a videotape.

Then, during playback, a burst signal (4) is generated from the TCI signal in the example in Figure 3 obtained by applying FM demodulation and emphasis.
is extracted, and a reproduced clock that follows the jitter of the reproduced signal is generated from this burst signal (4) by a PLL circuit.

[Problem to be solved by the invention]

However, in the past, the accuracy of the reproduced clock was not sufficient, and the digital signal processing during reproduction caused a deterioration in the quality of the reproduced image.

In view of the above, it is an object of the present invention to improve the accuracy of a reproduced clock and prevent deterioration in the quality of reproduced images.

[Means for Solving the Problems] A video signal recording and reproducing device according to the present invention records video signals (for example, a luminance signal (3) and a color difference signal (2)) at a predetermined period (IH), as shown in FIG. A burst signal for generating a reproduction clock (for example, a write clock WCK) when reproducing the video signal by time division multiplexing and reproducing the video signal by digital signal processing (for example, time axis correction, time compression, or time expansion). (6) for each period (IH
), the level of the burst signal (6) is added to the video signal (2, 3).
This level is greater than the level of .

[Effect]

According to the present invention, the recording level of the burst signal (6) can be increased, and the S/N ratio of the burst signal (6) can be improved during reproduction. Therefore, the accuracy of the reproduced clock is improved and deterioration in the quality of the reproduced image is prevented.

Also, unlike video signals, burst signals generally have a single frequency, so even if FM modulation is ultimately performed, for example, the frequency shift (dev
Even if iati○n) is set widely, the S/N ratio can be improved without causing problems such as overmodulation.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 1 and 2. In this example, the high-definition baseband signal is converted to TCI (Time Compressed In
The present invention is applied to a VTR that converts the signal into an FM signal and then performs FM modulation to record and reproduce the signal.

FIG. 1 shows the T(, I signal for l channel of this example,
Parts corresponding to those in FIG. 3 are designated by the same reference numerals.
In the figure, (5) is a negative polarity horizontal synchronizing pulse with a period of IH, and (6) has a frequency of approximately 5! J) It is a burst signal of about 5 waves at Iz, and the burst signal (6) is a time-compressed color difference signal C (PR or P,
) (2) and the time-expanded luminance signal Y(3) are time-division multiplexed. The frequency of the burst signal (6) is set to approximately the middle of the video signal band (approximately 10 Mtlz) before FM modulation. At the digital signal stage, the signal level of the luminance signal (3) (the difference between the white level and the black level) and the color difference signal (
The signal level (maximum amplitude) of 2) is 6 as in the conventional example.
bit) (26) or so and 6 to 7 bits (26 to 27)
The signal level (amplitude) of the burst signal (6) is set to about 9 bits (2g).

That is, in this example, the signal level of the burst signal (6) is set to be approximately 18 dB higher than the luminance signal (3) and approximately 12 dB higher than the color difference signal (2). Further, the peak level of the horizontal synchronizing pulse (5) is set to be equal to or smaller than the negative peak level of the burst signal (6). When the signal level of the burst signal (6) is set high as in this example, the S/N ratio during reproduction of the burst signal (6) is improved, the accuracy of the reproduced clock is improved, and the image quality of the reproduced image is improved. There is a benefit of preventing deterioration.

FIG. 2 shows the VTR of this example, and in this FIG.
7) is the recording unit as a whole, and (8) is the reproduction unit as a whole.This example has four heads each for recording and reproduction, and during recording, a different pair of recording heads is used for each l field. Recording is carried out using a recording head, and during playback, a different pair of playback heads is used for each field, but in the drawing, one recording head and one playback head are shown.

In the recording section (7) in FIG. 2, (9) and (10) are input terminals, (11) and (12) are CD A/D converters each having a sampling frequency of approximately 44.6 MHz, and (13) is a The time expansion circuit, <14) shows the time compression circuit, which is the luminance signal Y of the high-definition signal (bandwidth 20!).
J Hz) is supplied to the time expansion circuit (13) via the input terminal (9) and the A/D converter (1), and the time expansion circuit (13) time-expands the luminance signal Y by approximately twice. then 2
After dividing into channel signals, these two channel signals are supplied to one pair of input sections of the switch circuit (15) (only one channel of the switch circuit (15) etc. is shown).

In addition, the color difference signal C (PB and Pa) of the high-definition signal
(bandwidth 7), 11(z) to input terminal (lO) and A/
It is supplied to a time compression circuit (14) via a D converter (12), and the time compression circuit (14) converts the color difference signal C into approximately 1 line sequentially.
The time is compressed to /4 and supplied to the other pair of human power sections of the switch circuit (15). A TCI signal consisting of a luminance signal and a color difference signal for two channels is outputted from l pairs of output parts of this switch circuit (15), and this TCI signal is sent to a digital emphasis circuit (16) and a D/A converter (17).
to one input terminal of the adder.

When applying emphasis in the digital signal domain, there is the advantage that the emphasis characteristics can be easily set to desired characteristics.

(19) indicates a reference clock generation circuit that supplies the sampling clock SCK to the A/D converters (11) and (12), and (20) indicates a synchronization signal generation circuit that generates horizontal synchronization pulses and burst signals. By supplying the synchronous pulse and the burst signal to the other input terminal of the adder (18), the TCI signal of the example in FIG. 1 for two channels is outputted from the adder (18). Ko (7) TC
The r signal is transmitted through an emphasis circuit (21) and an FM modulation circuit (2
2) Recording is performed on a video tape (25) via a recording amplifier (23) and a recording head (24).In this case, the D/A conversion rate at the D/A converter (17) stage is burst. 3014 which is 6 times the signal frequency (5MHz)
It is set to Hz.

In the reproducing section (8), the output of the reproducing head (26) is connected to a reproducing amplifier (27), an FM demodulation circuit (28), a de-emphasis circuit (29), an A/D converter (30) and a TB.
TC via the C (time base collector) circuit (31)
C-fold signal and supply it to the input section of the switch circuit (32),
The center frequency of the output of the de-emphasis circuit (29) is 5.
It is supplied to a burst extraction circuit (35) and a synchronization signal detection circuit (36) through a MHz band-pass filter circuit (33) and a low-pass filter circuit (34), respectively, and the synchronization signal detection circuit (36) is a horizontal synchronization The burst gate pulse, which is set based on the pulse, is connected to the burst extraction circuit (35
). The burst signal (6) (about 5 waves at 5 M) Iz extracted by this burst extraction circuit (<35)
See Figure 1> is an injection type PLL (Phase L).
The clock signal is supplied to a write clock generation circuit (37) consisting of a clockedLoop) circuit. This write clock generation circuit (37) multiplies the frequency of the burst signal (6) six times to generate a write clock WCK with a frequency fs of approximately 30 Mz), and this write clock WCK
is supplied to the A/D converter (30) and the TBC circuit (31). The frequency fs of this write clock WCK varies following the jitter of the reproduced signal. Further, the TBC circuit (31) is supplied with a read clock RCK having a constant frequency from a reference oscillation circuit (not shown).

The switch circuit (32) is also supplied with a TCI signal as the output of a TBC circuit for another channel (not shown), and the switch circuit (32) receives the luminance signal Y portion of the TCI signal for two channels. Time compression circuit (38
), and the color difference signal C portion is supplied to the time expansion circuit (39).
supply to. The time compression circuit (38) reproduces the IH luminance signal from the TCI signal having the IH length for two channels, and the time expansion circuit (39) reproduces the IH luminance signal from the TCI signal having the IH length for two channels. Regenerate the color difference signal C (P'e and P,).The reproduced luminance signal Y and color difference signal C are sent to output terminals <42> and 43 via D/A converters <40> and (41), respectively. ).

In the recording section (7) of this example, as already mentioned, the TCI
Since the level of the burst signal (6) in the signal is set to be 12 dB to 13 dB higher than the video signal, the write clock generation circuit (37) of the playback section (8) has extremely good followability to the jitter of the playback signal. A good write clock WCK is generated. Therefore, A of the reproduction section (8)
Since the same output data as the input data of the D/A converter (17) of the recording section (7) is obtained from the /D converter (30), the TBC circuit (31), the time compression circuit (38) and the time Digital processing in the decompression circuit (39) accurately reproduces the human video signals Y and C to the recording section (7),
There is an advantage that the quality of the reproduced image does not deteriorate.

In addition, in this example, since the TCI signal in the example in Figure 1 is FM modulated, there is a question that a(l) of the burst signal (6) with a large level may cause problems such as overmodulation. Since the burst signal (6) is a sine wave or a rectangular wave with a single frequency that is about the middle of the video signal band, overmodulation will not occur even if the frequency shift during FM modulation is widened. ,
Since the video signal (especially the luminance signal Y) has a wide band and includes steep rises and falls at narrow intervals, if the level of the video signal is increased and the frequency shift during FM modulation is widened, overmodulation etc. are likely to occur. Become. Therefore,
There are relatively large restrictions on the range of frequency allocation and frequency shift when recording a video signal using FM, compared to the case of a burst signal (6).

Furthermore, since the recording section (7) of this example is provided with an emphasis circuit (16) in the digital signal domain, the emphasis circuit (21) in the analog signal domain can be omitted or the amount of emphasis can be extremely reduced. However, in this example, the level of the burst signal (6) is set high in advance, so the S/N ratio of the burst signal (6) after reproduction will not deteriorate. However, the emphasis circuit (I6) in the digital signal domain is omitted, and the emphasis circuit (21) in the analog signal domain has an emphasis mirror large*<t.

But that's fine.

It should be noted that the present invention is not limited to the above-described embodiments, and it goes without saying that various configurations may be adopted without departing from the gist of the present invention.

〔Effect of the invention〕

According to the present invention, since the level of the burst signal is higher than the level of the video signal, there is an advantage that the accuracy of the reproduced clock is improved and deterioration of image quality due to digital processing is prevented.

[Brief explanation of drawings]

FIG. 1 is a signal waveform diagram showing a TCI signal according to an embodiment of the present invention, FIG. 2 is a system diagram showing a VTR according to an embodiment, and FIG. 3 is a signal waveform diagram showing a conventional TCI signal. (2) is a color difference signal, (3) is a luminance signal, (5) is a horizontal synchronization pulse, (6) is a burst signal, (13) is a time expansion circuit, (14) is a time compression circuit, (20) is a synchronization The signal generation circuit, (31> is the TBC circuit, (37) is the write clock generation circuit, (38) is the time compression circuit, and (39) is the time expansion circuit. l - Thread No. 1 6) Agent Hitomatsu Hide Mori Kuma Figure 1 Figure 3

Claims (1)

[Claims] In addition to time-division multiplexing and recording of video signals at a predetermined period,
In a video signal recording and reproducing device that adds a burst signal within each cycle to generate a reproduction clock when reproducing the video signal by digital signal processing, the level of the burst signal is adjusted to the level of the video signal. A recording and reproducing device for a video signal, characterized in that the signal is made larger than the level.